Possible Duplicate:
OS X: using the keyboard to select an option in a message window / box?
On Snow Leopard 10.6 I used to be able to use tab and space to navigate between buttons and select one. I looked through the Accessibility preference pane and I have the "enable access for assistive devices" enabled, and everything else looks good - it is factory default.
Two examples of dialogs I can no longer navigate with tab / space:



Cmd-Dresults inDon't Save. – slhck Dec 19 '11 at 7:32